1. Field of the Invention
The present invention relates to a fluid pressure controller for supplying fluid pressurized at a regulated pressure to a fluid pressure apparatus such as a cylinder which is operated by the power of fluid pressure.
2. Description of the Related Art
For example, a pressure control valve as this type of fluid pressure controller is disclosed in Japanese Patent Publication No. 2589424, and the disclosures of which are herein incorporated by reference. As shown in FIG. 3, the pressure control valve 1 is provided with a main valve 3 for regulating the pressure of pressurized fluid supplied from a first pressurized fluid supply source 2. The opening degree of the main valve 3 is controlled by pilot pressure generated by an air supply solenoid valve 4a and an air discharge solenoid valve 4b. The air supply solenoid valve 4a and the air discharge solenoid valve 4b are controlled (turned on and turned off) by control signals outputted from a control circuit 5. A pressure sensor 6 detects the pressure of the fluid regulated by the main valve 3 and outputs a detection signal to the control circuit 5. The control circuit 5 performs a feedback control based on the detection signal.
A solenoid valve (three-way valve) 7 is provided between the air supply solenoid valve 4a and the air discharge solenoid valve 4b, and a pilot chamber (not shown) of the main valve 3. A second pressurized fluid supply source 9 is connected to the solenoid valve 7 via a pressure reducing valve 8.
In the conventional pressure control valve 1, since the solenoid valve 7 is provided between the air supply solenoid valve 4a and the air discharge solenoid valve 4b, and the pilot chamber of the main valve 3, when electric power supply to the pressure control valve is stopped, fluid communication between the air supply solenoid valve 4a and the air discharge solenoid valve 4b, and the pilot chamber is interrupted. Therefore, it is possible to regulate the pilot pressure in the pilot chamber of the main valve at an arbitrary pressure by the pressure reducing valve 8 provided externally to the main valve 3.
In the conventional pressure control valve 1, the external pressure reducing valve 8 regulates the pilot pressure in the pilot chamber of the main valve 3. Therefore, piping operations for providing a fluid communication passage A between the second pressurized fluid supply source 9 and the pressure reducing valve 8, and a fluid communication passage B between the pressure reducing valve 8 and the pressure control valve 1 are necessary.
Further, in the conventional pressure control valve 1, two pressure fluid supply sources (the first pressurized fluid supply source 2 and the second pressurized fluid supply source 9) are required. Additionally, the pressure reducing valve 8 is required. Therefore, many components are required in the system and the production cost thereof is high.
A general object of the present invention is to provide a fluid pressure controller for regulating fluid at a pressure substantially equal to an original pressure of a pressurized fluid supply source so as to provide a pilot pressure for a valve plug when electric power supply is stopped for some reasons.
A principle object of the present invention is to provide a fluid pressure controller which requires less piping operations and components in comparison with the conventional fluid pressure controller.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.